Lithium Batteries installation

[GUMPY]

57 minutes ago, nicknorman said:

The BMS settings can be changed, but you are prevented from doing so by needing the password. I think Fogstar will give you the password but will also note that your warranty will be invalidated for anything to do with cell problems arising from over or undercharge.

Yes this is what I should have said.

But if you don't have the password...........

[IanD]

26 minutes ago, nicknorman said:

This is presumably because the charger doesn’t know the battery current. Charging to a specified voltage without regard to the current results in potentially a very large variation in final SoC depending on the relationship between charger output and battery capacity. Certainly with a 2 hour absorb time the current is going to have fallen way off so the battery will be fully charged even if charged at a high C rate, but holding the voltage up at 14.2 for about 1:45 longer than necessary is not optimal. The battery may be slightly over charged.

 

As we have said, unless there is something wrong with the cells, they do not go out of balance so even with a crappy BMS that needs the voltage to be held up whilst balancing is taking place, in practice there will be no balancing going on during the 2 hours.

 

Victron don’t make cells. They just assemble batteries. So they, like so many other people, have adapted their LA chargers to roughly suit LiFePO4. Sub optimal!

 

 

True, but it's difficult to see what you can do better with a third-party drop-in LFP which doesn't talk to the MPPT (or alternator, or charger...) to control charging, via a controller like the Cerbo or similar -- or the same function running inside charger/inverter combos like the Multiplus/Quattro. The key is communication and having the BMS "in charge".

 

Which is of course what Victron recommend (battery BMS controls charging voltage and current) and what both my boat and yours do, because it's the optimum solution... 🙂

Edited February 16 by IanD

[nicknorman]

7 minutes ago, IanD said:

 

True, but it's difficult to see what you can do better with a third-party drop-in LFP which doesn't talk to the MPPT (or alternator!) to control charging, via a controller like the Cerbo or similar (or the same function inside charger/inverter combos like the Multiplus/Quattro).

 

Which is of course what Victron recommend (battery BMS controls charging voltage and current) and what both my boat and yours do, because it's the optimum solution... 🙂

Well it wouldn’t be too hard to link a Victron charger with something that measures battery current such as their BMV712 or Smartshunt. Then the charger would know when to stop charging (when the input to the battery fell to 5%C).

 

By the way, I checked the Fogstar recommended charge profile, they use EVE cells and have this to say about charging them - the ubiquitous 0.05C aka 5%C again.

Edited February 16 by nicknorman

[Guest]

1 hour ago, Naughty Cal said:

What heating system do you have?

 

Our Truma Combi 6E is hooked up to the Truma I Net system. You can remotely monitor battery voltages, van temperature, water temperature and remotely control the heating and hot water.

 

Alde wet system. The Swift 'Command system was supposed to do all that remote monitoring stuff allowing you to look at what was going on with the battery, activate the heating remotely , check the fridge etc etc.

 

But it was just pants. 

Edited February 16 by MJG

[GUMPY]

18 minutes ago, nicknorman said:

Well it wouldn’t be too hard to link a Victron charger with something that measures battery current such as their BMV712 or Smartshunt. Then the charger would know when to stop charging (when the input to the battery fell to 5%C).

Problem for me is that the 75/10 mppt controller only takes voltage and temperature, over the VE smart network,  from the smart Shunt not current 😟

 

[rusty69]

1 hour ago, nicknorman said:

Wrong. I would make it 5%. Assuming the system can charge at over 15A. Although it also depends on what voltage settings you have set.

Ok. Thanks. The absorbtion is usually set between 13.9 and 14.1 Volts for a 10 minute duration. So, if I want to use the tail current setting, it should be set to 5% of my 280Ahr LI + 100 Ahr LA bank = 19 A, or 5 % of 280Ahr = 14A? The chargers are capable of 30A each, and there are 2.

1 hour ago, IanD said:

Victron don't recommend using a tail current for LFP batteries -- do Fogstar? From the MPPT manual:

 

Default settings for LiFePO4 batteries
The default absorption voltage is to 14.2V (28.4V) and the absorption time is fixed and set to 2 hours. The float voltage is
set at 13.5V (27V). Equalization is disabled. The tail current is set to 0A, this so that the full absorption time is available
for cell balancing. The temperature compensation is disabled and the low temperature cut off is set to 5. These settings are
the recommended settings for LiFePO4 batteries, but they can be adjusted if the battery manufacturer specifications advise
otherwise.

Thanks. Yes, I remember reading that just before I put my own settings in. Dunno what fogstar recommend, I don't have one of their batteries or cells (yet).

[nicknorman]

9 minutes ago, rusty69 said:

Ok. Thanks. The absorbtion is usually set between 13.9 and 14.1 Volts for a 10 minute duration. So, if I want to use the tail current setting, it should be set to 5% of my 280Ahr LI + 100 Ahr LA bank = 19 A, or 5 % of 280Ahr = 14A? The chargers are capable of 30A each, and there are 2.

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

[rusty69]

2 minutes ago, nicknorman said:

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

Maybe I'll just ditch the LA. Seems so much easier.

[IanD]

4 minutes ago, nicknorman said:

Ah well here we run headlong into the problem of mixing batteries of different chemistries. The LA wants a tail current setting of 2% or less, the Li wants a tail current setting of 5%. Which is appropriate? There is only one way to find out.

 

FIGHT!

Aren't the recommended absorption voltages different too? And LA voltages vary with temperature but LFP don't?

[rusty69]

1 minute ago, IanD said:

Aren't the recommended absorption voltages different too? And LA voltages vary with temperature but LFP don't?

Yes. My LA has a recommended absorbtion of 14.4V. I tend to stick it on the battery charger once a week and isolate the LI to satisfy that requirement, though understand it is less than ideal.

[rusty69]

22 hours ago, nicknorman said:

Not totally sure, I think it is an epever PWM controller. Very cheap, but it has the interface for the MT50 display which can be used to adjust all the settings.

 

I have been thinking of getting an MPPT controller but there is not a huge advantage when the Vmp of the panel is only around 16v

I'm sure you know all this, being an electronic genius, however I thought I would share it here anyway. Whilst investigating my optimum tail current termination valuation vs absorption voltage, I came across this quote from nordkyn:

 

Quote

The worst ripple voltage is produced by solar PWM charge controllers, followed by old-style transformer/rectifier battery chargers, which should not be associated with lithium batteries

 

 

From this page on tinterweb

 

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

Edited February 17 by rusty69
not Rod

[nicknorman]

19 minutes ago, rusty69 said:

I'm sure you know all this, being an electronic genius, however I thought I would share it here anyway. Whilst investigating my optimum tail current termination valuation vs absorbrion voltage, I came across this quote from Rod:

 

 

 

From this page on tinterweb

 

https://nordkyndesign.com/charging-marine-lithium-battery-banks/

Yes it’s a good point. I got the Li battery in the early winter and so far, what with snow on the panel, the panel blowing over etc etc, the solar has never got even close to fully charging the battery. But in summer, it will do. Which is a good reason for getting an MPPT controller!

 

It’s actually also a good point in relation to charging with an alternator which is intrinsically fairly rippley. In our case the Combi input capacitors act to smooth out the ripples a lot, but a system with just an alternator and no large capacitors in the system, is going to have plenty of ripple. At some point I might take my ‘scope down to the boat and check out the ripple with and without the Combi in circuit. Probably the ripple won’t be that bad at lower SoC due to the very low internal resistance of the Li, but it will be interesting  see the ripple as the batteries approach 100% and the current is tapering.

[peterboat]

22 hours ago, nicknorman said:

My point was a general one and not specifically all about me(!) - the point being that charging to a specified limit voltage (which is what solar controllers do) can result in either under or over charging. The latter being more of an issue for Li. Of course it is not an issue for LA.

 

But to continue with my particular issue I have a 100Ah Li battery and a 100W solar panel. So even in summer on a sunny day (in Scotland) it only is likely to charge at about 5%C and in winter much slower, 1%C if I’m lucky!

 

In winter I use it to run the telly and Sat box and the electric blanket for Friday evening and Saturday evening. So that probably takes out 40% of capacity. Meanwhile it may get between zero and 5% back in during the day in winter. So I leave on Sunday with it quite low and hope that when I return on Friday evening it will be replenished - otherwise I need to get the genny going. Then as we move towards spring, it gets more charge each day and at some point - varying each week according to the weather, it is going to get to 100% during the week and I am going to be using much less power of an evening. So there is a risk of it being overcharged.

 

All of which is simply to say that solar controllers are not optimised to Li charging.

I have always charged by solar on my Lithiums, however I do have things running, the fan on the toilet and the fridge freezer  so this seems to keep things correct on my system. Even still I have seen my midnite controller showing no charge and the batteries at the correct voltage, maybe the quality of the controller is what counts?

[GUMPY]

Some waffle about setting MPPT controllers for lithium.

 

 

[MtB]

56 minutes ago, GUMPY said:

Some waffle about setting MPPT controllers for lithium.

 

 

 

 

37 minutes!!!!!!

 

I'm watching it at double speed and not seen anything useful yet....

 

But hark, at 2 mins 40 sec I hear "Lets get to it!" and he does! 

 

Back to watching now....

 

[WulfNut]

On 16/02/2024 at 13:11, nicknorman said:

The BMS settings can be changed, but you are prevented from doing so by needing the password. I think Fogstar will give you the password but will also note that your warranty will be invalidated for anything to do with cell problems arising from over or undercharge.

888888  ? From 12v group

Fogstar say that the warranty will be valid unless the damage is caused by the settings you have changed.  Obviously they do not want people changing temp settings and what not.  I would add that if anyone thinks they need to change any settings it would always be best to email fogstar and ask them if the setting you want to change is safe.  I do not want anyone ruining what is an expensive battery.

Edited May 21 by WulfNut

[Tony1]

On 16/02/2024 at 11:29, nicknorman said:

 

For my caravan battery (which is left unattended without significant power drain for days or weeks at a time), I have set the solar to 13.9v with very short absorption time, and float of 13.25v hoping that that is not going to result in the battery being held “up the knee” too far every day. But it is not ideal because when I am using the caravan in summer, it will take longer to recharge at that voltage.

 

 

My old charging management setup might have gone some way to ameliorate the challenge of lithiums being held at high states of charge for long periods.

I used a BMV712 and set its relay to send a 12v signal when the SoC reached 85%. It was your good self who gave me the instructions I needed to set it up.

The MPPTs have an input (I think its labelled 'BMS') that is designed to accept this 12v signal/input, and when they receive the signal they will switch themselves off safely. And conversely, when the SoC falls below the user-nominated value (say 50%), the BMV712 sends a signal that causes the MPPTs to switch on again. 

It all depends on whether the MPPTs in question have an input for 'remote', BMS, or similar.

If they do, you could use a BMV712 as I did, to effectively keep them switched off until the batteries get a chance to discharge a bit. 

 

I stopped using this setup as it seemed simpler to just use a charging voltage of about 13.8 or 13.9v (which mostly gets the batteries to about 85% anyway, and is a lot simpler)- and because the boat is seldom left alone for more than a few days. 

But if I was ever to leave it for weeks on end, I would consider using my spare BMV712, and reinstating my old SoC-based management of the MPPTs.

 

I still feel very slightly uneasy on a hot summer day, when I know the panels are receiving almost 50 amps of solar power and I then just switch them off, with so much energy coming into them, but it I guess Victron wouldn't give you this feature to disable the MPPT (even when charging) if its wasn't safe.

 

 

Edited May 21 by Tony1

[nicknorman]

13 minutes ago, Tony1 said:

 

My old charging management setup might have gone some way to ameliorate the challenge of lithiums being held at high states of charge for long periods.

I used a BMV712 and set its relay to send a 12v signal when the SoC reached 85%. It was your good self who gave me the instructions I needed to set it up.

The MPPTs have an input (I think its labelled 'BMS') that is designed to accept this 12v signal/input, and when they receive the signal they will switch themselves off safely. And conversely, when the SoC falls below the user-nominated value (say 50%), the BMV712 sends a signal that causes the MPPTs to switch on again. 

It all depends on whether the MPPTs in question have an input for 'remote', BMS, or similar.

If they do, you could use a BMV712 as I did, to effectively keep them switched off until the batteries get a chance to discharge a bit. 

 

I stopped using this setup as it seemed simpler to use a charging voltage of about 13.8 or 13.9v (which mostly gets the batteries of about 85%), and because the boat is seldom left alone for more than a few days. 

But if I was ever to leave it for weeks on end, I would consider using my spare BMV712, and reinstating my old SoC-based management of the MPPTs.

 

I still feel very slightly uneasy on a hot summer day, when I know the panels are receiving almost 50 amps of solar power and I then just switch them off, with so much energy coming into them, but it I guess Victron wouldn't give you this feature to disable the MPPT (even when charging) if its wasn't safe.

 

 

Yes I really should take my own advice and do it properly! I’ve just left the caravan for a week, the battery was close to 100% following a few days of sunshine, so I simply turned off the charger using the App.

 

But I already have a BMV712 installed, so it’s crazy not to use that! Thank you for pointing out my stupidity!

 

But there is of course another thing to contemplate, the blue smart solar and the BMV712 support VE.Smart Networking over Bluetooth. If the BMV sent SoC data to the Solar there would be scope for the solar to stop and start charging at specified SoCs. However as far as I can tell, SoC data is not shared over the network, only voltage and current. This seems a foolish omission! So it looks like I’m stuck with making up a VE.Direct cable to operate the solar from the BMV relay.

[GUMPY]

I switch my Victron MPPT off remotely if I am leaving the van for a while and the battery is near 100%.

Problem I have is which % to believe, Smart Shunt that is reading 96% or the BMS reading 99%. BMS doesn't detect any current under about half an amp so doesn't always react to charge from the solar 😱 

[nicknorman]

3 minutes ago, GUMPY said:

I switch my Victron MPPT off remotely if I am leaving the van for a while and the battery is near 100%.

Problem I have is which % to believe, Smart Shunt that is reading 96% or the BMS reading 99%. BMS doesn't detect any current under about half an amp so doesn't always react to charge from the solar 😱 

Yes I think the Fogstar BMS is pretty inaccurate when it comes to SoC. I tend to believe the BMV712. I get the battery to 100% every now and then to synchronise the SoC, and see that the BMV is much closer than the BMS.

[GUMPY]

I wonder how many high/low cell voltage alerts others have in their logs? Mine is at 16 high 1 low but then it rarely gets discharged lower than about 40% 

[nicknorman]

7 minutes ago, GUMPY said:

I wonder how many high/low cell voltage alerts others have in their logs? Mine is at 16 high 1 low but then it rarely gets discharged lower than about 40% 

I’ll try to remember to look next weekend. But I think the Fogstar BMS is set very conservatively, it stops charging at I think 3.55v/cell as opposed to the more normal 3.65v. So if a cell has hit 3.55v this is nothing to get excited about!

 

Its a shame you have the smart shunt as opposed to the BMV712, the latter has the relay which could be used to control the solar, the former doesn’t.

[GUMPY]

11 minutes ago, nicknorman said:

Its a shame you have the smart shunt as opposed to the BMV712, the latter has the relay which could be used to control the solar, the former doesn’t.

I wanted something that would fit in the battery box and no meters in the van, also something I can easily remove as and when I sell,  hence my choice.

The solar panel and MPPT controller can be left all the rest of the kit will be coming out.

[Tony1]

1 hour ago, nicknorman said:

Yes I really should take my own advice and do it properly! I’ve just left the caravan for a week, the battery was close to 100% following a few days of sunshine, so I simply turned off the charger using the App.

 

But I already have a BMV712 installed, so it’s crazy not to use that! Thank you for pointing out my stupidity!

 

But there is of course another thing to contemplate, the blue smart solar and the BMV712 support VE.Smart Networking over Bluetooth. If the BMV sent SoC data to the Solar there would be scope for the solar to stop and start charging at specified SoCs. However as far as I can tell, SoC data is not shared over the network, only voltage and current. This seems a foolish omission! So it looks like I’m stuck with making up a VE.Direct cable to operate the solar from the BMV relay.

 

 

Heaven only knows where I put my VE cables when I stopped using that setup, but hopefully I can find them again if/when I want to reinstate the SoC management. 

One thing I do recall was that to use the SoC parameter of the BMV for this purpose, I had to invert the relay, and think I used it 'back to front', so to speak.

Apologies as this is a garbled half remembered explanation, but I had to pretend that the 85% was the low SoC trigger point, and 50% was the high one, to make it work properly. I think that was because the BMV712 relay cant be set to switch at high SoC, only low SoC.  I think the relay was NC, but cant be sure. Hopefully with your expert knowledge you'll grasp that rather tenuous explanation. 

 

You explained all this to me properly at the time, and unfortunately I shall have to prevail upon your expertise once again, if I ever decide to reinstate that setup! 

 

Edited May 21 by Tony1

[GUMPY]

15 hours ago, WulfNut said:

888888  ? From 12v group

👍

5 hours ago, nicknorman said:

I think the Fogstar BMS is set very conservatively, it stops charging at I think 3.55v/cell as opposed to the more normal 3.65v. So if a cell has hit 3.55v this is nothing to get excited about!

Looking in the advanced settings it appears to be 3.6v 😉